CHAPTER 14: Genes in Action
Essential Questions:
What is a Mutation?
What Causes Mutation?
What is the origin of genetic differences among organisms?
What types of mutations are possible?
How can genetic change occur on a larger scale?
How will Modern Technology in DNA affect us?
Gene Mutations
A Mutation is a change in the
sequence of DNA bases within
a gene
What Causes Mutations:
Mutations can be
spontaneous or caused by
environmental influences
called MUTAGENS.
Origins of Genetic Difference
MUTATION is the origin
differences among
organisms
For the most part, genetic
differences among
organisms originate as
some kind of mutation.
A genetic mutant is an
individual whose DNA or
Effects of Mutations
Because of the way DNA is translated, a
mutation can have many possible effects.
A small change in DNA may effect just
one Amino Acid in the protein that results
from a gene
A mutation may have no effect, or may
harm or help in some way.
Mutations are noticed when they cause an
unusual trait or disease, such as sickle
cell anemia.
Many mutations may go unnoticed.
Types of Mutations
Changes to the letters (A,C,T,G bases) in the
DNA can result in 2 types of mutation
Point Mutation
A change to ONE letter (base) in the DNA
May cause change to protein, may not
Frameshift Mutation
Addition of a new letter (base) in the DNA sequence
A deletion of a letter (base) in the DNA
Both shift the DNA so it changes how the Codons are
read
BIG changes to protein
Types of Point Mutations
Silent Mutation:
The change in the codon results in the
same amino acid
Ex: UAU  UAC
Both code for Tyrosine
Nonsense Mutation:
A codon is changed to a STOP Codon
Resulting protein may be too short to
function
Ex: UAC  UAG
( a STOP Codon )
Missense Mutation:
Involves the substitution of a different
amino acid
The result MAY be a protein that
cannot reach its final shape
Ex: Hbs causes sickle-cell disease
Sickle cell anemia
Hemoglobin protein in red blood cells
Strikes 1 out of 400 African Americans
Limits activity, painful & may die young
Point Mutations
One BASE change
Can change the meaning of the whole protein
THEFATCATANDTHEREDRATRAN
THEFATCARANDTHEREDRATRAN
OR
THEFATCATENDTHEREDRATRAN
Does this change
the sentence?
A LITTLE!
Mutations as Changes in Genes
Changes in a DNA sequence may affect
the results of genes in many ways.
A mutation is SILENT when it has no
effect on a gene’s function.
Point Mutations are often silent because
the genetic code is REDUNDANT-each
Amino Acid has multiple codons.
A MISSENSE or Replacement mutation
results when a codon is changed such that
the new codon codes for a different
Amino Acid.
A NONSENSE Mutation results when a
mutation forms a STOP codon
Point Mutations
Silent Mutation: 1 change to Nucleotide
NO change to Protein
AUG CGU GUA UAC GCA UGC GAG UGA
Met Arg Val Tyr Ala Cys Glu Stop
AUG CGU GUA UAC GCU UGC GAG UGA
Met Arg Val Tyr Ala Cys Glu Stop
Point Mutations
Missense Mutation: 1 Nucleotide Change
Changes Amino Acid
AUG CGU GUA UAC GCA UGC GAG UGA
Met Arg Val Tyr Ala Cys Glu Stop
AUG CGU GUA UAC GUA UGC GAG UGA
Met Arg Val Tyr Val Cys Glu Stop
Point Mutations
Nonsense Mutation: 1 Nucleotide Change
Changes to STOP Codon
AUG CGU GUA UAC GCA UGC GAG UGA
Met Arg Val Tyr Ala Cys Glu Stop
AUG CGU GUA UAA GCA UGC GAG UGA
Met Arg Val STOP
Frameshift Mutations
The Reading Frame of a sequence depends on the
starting point for reading. An insertion or deletion
can shift the reading frame, or cause a
FRAMESHIFT.
In Frameshift mutations, the remaining sequence
may be “read” as different codons.
An insertion or deletion of many codons is likely to
disrupt the resulting protein’s structure and function.
Frameshift Mutations
Add or Delete one or more bases
Changes the meaning of the whole protein
THE FAT CAT AND THE RED RAT RAN
Add a Nucleotide
THE FAT CAN TAN DTH ERE DRA TRA N
OR Delete
THE FAT CAA NDT HER EDR ATR AN
Frameshift Mutations
Addition: Add one or more bases
AUG CGU GUA UAC GCA UGC GAG UGA
Met Arg Val Tyr Ala Cys Glu Stop
Major changes in Reading Frame and Amino Acid Sequence
AUG CGU GUA UAC GUC AUG CGA GUG A
Met Arg Val Tyr
Val Met Arg Val A
Frameshift Mutations
Deletion: Delete one or more bases
AUG CGU GUA UAC GCA UGC GAG UGA
Met Arg Val Tyr Ala Cys Glu Stop
Major changes in Reading Frame and Amino Acid Sequence
AUG CGU GUA UAC GAU GCG AGU GA?
Met Arg Val Tyr
Asp Ala Ser GA
Deletion Mutation: Cystic Fibrosis
Some Common Genetic Diseases
Huntington’s Disease: Autosomal dominant
Neuromuscular disease; degeneration of muscle, onset in early 30’s.
Cystic Fibrosis: Autosomal Recessive;
Defective Protein is made that creates excess mucus; clogs lungs.
Color Blindness: Sex-linked recessive
Inablity to distinguish colors (8% of male population)
Hemophilia: Sex-linked recessive
Inablity of blood to clot
Muscular Dystrophy: Sex-linked recessive
Loss of muscle that begins in early childhood
Tay-Sach’s Disease : Autosomal Recessive
Degeneration of Central Nervous System; infant mortality
LARGE-SCALE GENETIC CHANGE
How can genetic change
occur on a larger scale?
Very large-scale genetic
change can occur by
misplacement,
recombination, or
multiplication of entire
chromosomes.
Chromosomal Mutations
During meiosis, chromosomes
pair up and may undergo
CROSSOVER.
Usually, the result is an equal
exchange of alleles between
homologous chromosomes.
Errors in the exchange can
cause CHROMOSOMAL
MUTATIONS.
Changes in Chromosome Structure
Chromosome Mutation: A change in
chromosome structure
4 Types of Chromosomal Mutations:
Inversion
Translocation
Deletion
Duplication
Chromosomal Deletion:
Williams Syndrome
Deletions occur when a single break
causes a lost end piece, or two
breaks result in a loss in the interior.
Children have a pixie look (turnedup noses, wide mouth, small chin,
large ears)
Poor academic skills, good verbal
and musical abilities. Skin ages
prematurely from lack of the gene
that controls the production of
elastin (also affects cardiovascular
health).
Chromosomal Duplication: Dup15
Duplication results in a
chromosome segment being
repeated in the same
chromosome
An inverted duplication in
chromosome 15 causes Dup 15
syndrome
Poor muscle tone, mental
retardation, seizures, curved
spine, and autistic
characteristics
Chromosome Translocation :
Alagille Syndrome
Translocation is exchange of
chromosomal segments between
two, non-homologous
chromosomes.
Ex: Alagille syndrome
results from a deletion of
chromosome 20 or a
translocation that disrupts an
allele on chromosome 20.
Distinctive face,
abnormalities of eyes &
internal organs, and severe
itching.
Chromosome Inversion
Inversion involves a segment of a chromosome being turned 180
degrees
The reverse sequence of alleles can alter gene activity.
Crossing-over between inverted and normal chromosomes
can cause DUPLICATIONS and DELETIONS
Changes in Chromosome Number
NONDISJUNCTION occurs when:
In Meiosis I, homologous pair both
go into the same daughter cell or in
Meiosis II, the sister chromatids
both go into the same gamete.
Example: Trisomy 21 Down Syndrome
is a GENETIC DISORDER caused by
the presence of all or part of a third
copy of chromosome 21. It is
associated with growth delays, and
mild to moderate intellectual disability.
Changes in Chromosome Number
NONDISJUNCTION occurs when:
In Meiosis I, homologous pair
both go into the same daughter
cell or in Meiosis II, the sister
chromatids both go into the
same gamete.
Example: Trisomy 21 Down
Syndrome is a GENETIC
DISORDER caused by the presence
of all or part of a third copy of
chromosome 21. It is associated with
growth delays, and mild to moderate
intellectual disability.
EFFECTS OF GENETIC
CHANGE
What are the possible effects of
mutations?
The results of genetic change may
be harmful, beneficial, or neutral;
most changes are neutral and may
not be passed on to offspring.
Most genetic changes will cause
NO change in the appearance or
function of organisms.
Mutations that occur in Gametes
can be passed on to offspring, but
mutations in body cells affect only
the individual in which they occur.
DNA Technology and Modern
Medicine
The Human Genome Project Decoded an entire
length of DNA in 2003
The Genetic Sequencing allows for
improvements in the detection and treatment of
genetic disease and cancer.
Gene Therapy is a technology in which good
copies of a gene are introduced into those
individuals affected by genetic disease
CH11 GENES IN ACTION
BOOM THAT’S IT!!!!